Vehicle brake system and diagnostic method for determining a leak in one or more three-way valves

ABSTRACT

A diagnostic method to identify a leak in a three-way valve for a vehicle brake system having a remote master cylinder which includes the steps of: (1) providing a pedal simulator having pressure medium; (2) de-energizing a secondary three-way valve; (3) retracting a dual acting plunger to the home position to drop the pressure in the boost circuit to zero while also monitoring the pressure at the output of a fluid separator via a secondary master cylinder pressure sensor; (4) determining a rate of pressure reduction at the output of a fluid separator via a secondary master cylinder pressure sensor; and (5) identifying a leak in at least one of a primary three-way valve and the secondary three way valve if the rate of pressure reduction is equal to or higher than a pre-determined rate.

TECHNICAL FIELD

The present disclosure generally relates to a vehicle brake system and adiagnostic system for determining the existence of a leak in one or morethree-way valves.

BACKGROUND

Vehicles are commonly slowed and stopped with hydraulic brake systems.These systems vary in complexity but a base brake system typicallyincludes a brake pedal, a tandem master cylinder, fluid conduitsarranged in two similar but separate brake circuits, and wheel brakes ineach circuit. The driver of the vehicle operates a brake pedal which isconnected to the master cylinder. When the brake pedal is depressed, themaster cylinder generates hydraulic forces in both brake circuits bypressurizing brake fluid. The pressurized fluid travels through thefluid conduit in both circuits to actuate brake cylinders at the wheelsto slow the vehicle.

Base brake systems typically use a brake booster which provides a forceto the master cylinder which assists the pedal force created by thedriver. The booster can be vacuum or hydraulically operated. A typicalhydraulic booster senses the movement of the brake pedal and generatespressurized fluid which is introduced into the master cylinder. Thefluid from the booster assists the pedal force acting on the pistons ofthe master cylinder which generate pressurized fluid in the conduit influid communication with the wheel brakes. Thus, the pressures generatedby the master cylinder are increased. Hydraulic boosters are commonlylocated adjacent the master cylinder piston and use a boost valve tocontrol the pressurized fluid applied to the booster.

Braking a vehicle in a controlled manner under adverse conditionsrequires precise application of the brakes by the driver. Under theseconditions, a driver can easily apply excessive braking pressure thuscausing one or more wheels to lock, resulting in excessive slippagebetween the wheel and road surface. Such wheel lock-up conditions canlead to greater stopping distances and possible loss of directionalcontrol.

Advances in braking technology have led to the introduction of Anti-lockBraking Systems (ABS). An ABS system monitors wheel rotational behaviorand selectively applies and relieves brake pressure in the correspondingwheel brakes in order to maintain the wheel speed within a selected sliprange to achieve maximum braking force. While such systems are typicallyadapted to control the braking of each braked wheel of the vehicle, somesystems have been developed for controlling the braking of only aportion of the plurality of braked wheels.

Electronically controlled ABS valves, comprising apply valves and dumpvalves, are located between the master cylinder and the wheel brakes.The ABS valves regulate the pressure between the master cylinder and thewheel brakes. Typically, when activated, these ABS valves operate inthree pressure control modes: pressure apply, pressure dump and pressurehold. The apply valves allow pressurized brake fluid into respectiveones of the wheel brakes to increase pressure during the apply mode, andthe dump valves relieve brake fluid from their associated wheel brakesduring the dump mode. Wheel brake pressure is held constant during thehold mode by closing both the apply valves and the dump valves.

To achieve maximum braking forces while maintaining vehicle stability,it is desirable to achieve optimum slip levels at the wheels of both thefront and rear axles. During vehicle deceleration different brakingforces are required at the front and rear axles to reach the desiredslip levels. Therefore, the brake pressures should be proportionedbetween the front and rear brakes to achieve the highest braking forcesat each axle. ABS systems with such ability, known as Dynamic RearProportioning (DRP) systems, use the ABS valves to separately controlthe braking pressures on the front and rear wheels to dynamicallyachieve optimum braking performance at the front and rear axles underthe then current conditions.

A further development in braking technology has led to the introductionof Traction Control (TC) systems. Typically, valves have been added toexisting ABS systems to provide a brake system which controls wheelspeed during acceleration. Excessive wheel speed during vehicleacceleration leads to wheel slippage and a loss of traction. Anelectronic control system senses this condition and automaticallyapplies braking pressure to the wheel cylinders of the slipping wheel toreduce the slippage and increase the traction available. In order toachieve optimal vehicle acceleration, pressurized brake fluid is madeavailable to the wheel cylinders even if the master cylinder is notactuated by the driver.

During vehicle motion such as cornering, dynamic forces are generatedwhich can reduce vehicle stability. A Vehicle Stability Control (VSC)brake system improves the stability of the vehicle by counteractingthese forces through selective brake actuation. These forces and othervehicle parameters are detected by sensors which signal an electroniccontrol unit. The electronic control unit automatically operatespressure control devices to regulate the amount of hydraulic pressureapplied to specific individual wheel brakes. In order to achieve optimalvehicle stability, braking pressures greater than the master cylinderpressure must quickly be available at all times.

Brake systems may also be used for regenerative braking to recaptureenergy. An electromagnetic force of an electric motor/generator is usedin regenerative braking for providing a portion of the braking torque tothe vehicle to meet the braking needs of the vehicle. A control modulein the brake system communicates with a powertrain control module toprovide coordinated braking during regenerative braking as well asbraking for wheel lock and skid conditions. For example, as the operatorof the vehicle begins to brake during regenerative braking,electromagnet energy of the motor/generator will be used to applybraking torque (i.e., electromagnetic resistance for providing torque tothe powertrain) to the vehicle. If it is determined that there is nolonger a sufficient amount of storage means to store energy recoveredfrom the regenerative braking or if the regenerative braking cannot meetthe demands of the operator, hydraulic braking will be activated tocomplete all or part of the braking action demanded by the operator.Preferably, the hydraulic braking operates in a regenerative brakeblending manner so that the blending is effectively and unnoticeablypicked up where the electromagnetic braking left off. It is desired thatthe vehicle movement should have a smooth transitional change to thehydraulic braking such that the changeover goes unnoticed by the driverof the vehicle.

Some braking systems are configured such that the pressures at each ofthe wheel brakes can be controlled independently (referred to as amultiplexing operation) from one another even though the brake systemmay include a single source of pressure. Thus, valves downstream of thepressure source are controlled between their open and closed positionsto provide different braking pressures within the wheel brakes. Suchmultiplex systems, which are all incorporated by reference herein, aredisclosed in U.S. Pat. No. 8,038,229, U.S. Patent ApplicationPublication No. 2010/0016083, U.S. Patent Application Publication No.2012/0013173, and U.S. Patent Application Publication No. 2012/0136261.

The above information disclosed in this Background section is only forenhancement of understanding of the background of the invention, andtherefore, it may contain information that does not form the prior artthat is already known in this country to a person of ordinary skill inthe art.

SUMMARY

In a first embodiment of the present disclosure, a diagnostic method fora vehicle brake system is provided which identifies a leak in athree-way valve within the vehicle brake system. The diagnostic methodincludes the steps of: (1) providing a pedal simulator having a pressuremedium within a simulation chamber of the pedal simulator; (2)de-energizing a secondary three-way valve; (2) retracting a plunger to ahome position within a plunger assembly to reduce boost circuit pressureto zero while also monitoring the pressure at an output of a fluidseparator via a secondary master cylinder pressure sensor; (3)determining a rate of pressure reduction at the output of a fluidseparator via the secondary master cylinder pressure sensor; and (4)identifying a leak in at least one of a primary three-way valve and thesecondary three-way valve if the rate of pressure reduction is equal toor greater than a pre-determined rate. The pre-determined rate may, butnot necessarily, be defined to be about 7 bar/100 msec.

The vehicle brake system which implements the aforementioned diagnosticmethod may include a reservoir and a master cylinder which are disposedin a first module while the pedal simulator, a simulator test valve, andthe plunger assembly of the vehicle brake system are disposed in asecond module which is separate from the first module. As a result ofthe dual module design having a remote master cylinder in the firstmodule, this vehicle brake system may be easier to package within avehicle due to space limitations in a vehicle. Moreover, the vehiclebrake system of the present disclosure includes a primary three-wayvalve and a secondary three-way valve. The primary three-way valve is influid communication with a second wheel brake and a third brake whilethe secondary three-way valve is in fluid communication with a firstwheel brake and a fourth wheel brake.

With respect to the diagnostic method provided above, it is understoodthat the step of identifying a leak in at least one of the primary andsecondary three-way valves may be performed via a signal transmittedfrom the ECU to a vehicle user interface. Moreover, the step ofproviding a pedal simulator having pressure medium disposed with achamber of the pedal simulator, may further include the steps of: (1)energizing a pumping valve, the secondary three-way valve, and aplurality of apply valves disposed in the second module; (2) energizinga simulator valve disposed within the second module to enablebi-directional flow of pressure medium within the simulator valve; (3)applying and retracting the plunger in the plunger assembly whilekeeping the simulator valve energized, until pressure within a secondoutput pressure chamber of the master cylinder reaches a pre-determinedlevel; and (4) de-energizing the simulator valve while completing thestroke of the plunger in the plunger assembly once pressure in thesecond output pressure chamber of the master cylinder reaches thepredetermined level. The pre-determined pressure level for the secondoutput pressure chamber may, but not necessarily be about 1.5 bar.

The plunger assembly includes a motor which is actuated by an electroniccontrol module and the motor causes the plunger in the plunger assemblyto cycle within a first pressure chamber in the plunger assembly.Moreover, the second module of the aforementioned vehicle brake systemhouses every hydraulic valve of the vehicle brake system. Lastly, thepressure medium implemented in the aforementioned method and system may,but not necessarily, be brake fluid.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present disclosure willbe apparent from the following detailed description, best mode, claims,and accompanying drawings in which:

FIG. 1A is a first schematic diagram of a first braking system accordingto the present disclosure;

FIG. 1B is a second schematic diagram of the first braking system inFIG. 1A wherein the simulator piston moves rear/right-ward as theplunger in the plunger assembly advances (moves forward/left) andapplies pressure to the boost circuit;

FIG. 2A is a schematic diagram of a second braking system according tothe present disclosure where the simulator is filled with pressuremedium; and

FIG. 2B is a schematic diagram of a second braking system according tothe present disclosure where the simulator emptied of pressure mediumand the piston is advanced within the simulator.

Like reference numerals refer to like parts throughout the descriptionof several views of the drawings.

DETAILED DESCRIPTION

Reference will now be made in detail to presently preferredcompositions, embodiments and methods of the present disclosure, whichconstitute the best modes of practicing the present disclosure presentlyknown to the inventors. The figures are not necessarily to scale.However, it is to be understood that the disclosed embodiments aremerely exemplary of the present disclosure that may be embodied invarious and alternative forms. Therefore, specific details disclosedherein are not to be interpreted as limiting, but merely as arepresentative basis for any aspect of the present disclosure and/or asa representative basis for teaching one skilled in the art to variouslyemploy the present disclosure.

Except in the examples, or where otherwise expressly indicated, allnumerical quantities in this description indicating amounts of materialor conditions of reaction and/or use are to be understood as modified bythe word “about” in describing the broadest scope of the presentdisclosure. Practice within the numerical limits stated is generallypreferred. Also, unless expressly stated to the contrary: percent,“parts of,” and ratio values are by weight; the description of a groupor class of materials as suitable or preferred for a given purpose inconnection with the present disclosure implies that mixtures of any twoor more of the members of the group or class are equally suitable orpreferred; the first definition of an acronym or other abbreviationapplies to all subsequent uses herein of the same abbreviation andapplies mutatis mutandis to normal grammatical variations of theinitially defined abbreviation; and, unless expressly stated to thecontrary, measurement of a property is determined by the same techniqueas previously or later referenced for the same property.

It is also to be understood that this present disclosure is not limitedto the specific embodiments and methods described below, as specificcomponents and/or conditions may, of course, vary. Furthermore, theterminology used herein is used only for the purpose of describingparticular embodiments of the present disclosure and is not intended tobe limiting in any manner.

It must also be noted that, as used in the specification and theappended claims, the singular form “a,” “an,” and “the” comprise pluralreferents unless the context clearly indicates otherwise. For example,reference to a component in the singular is intended to comprise aplurality of components.

The term “comprising” is synonymous with “including,” “having,”“containing,” or “characterized by.” These terms are inclusive andopen-ended and do not exclude additional, unrecited elements or methodsteps.

The phrase “consisting of” excludes any element, step, or ingredient notspecified in the claim. When this phrase appears in a clause of the bodyof a claim, rather than immediately following the preamble, it limitsonly the element set forth in that clause; other elements are notexcluded from the claim as a whole.

The phrase “consisting essentially of” limits the scope of a claim tothe specified materials or steps, plus those that do not materiallyaffect the basic and novel characteristic(s) of the claimed subjectmatter.

The terms “comprising”, “consisting of”, and “consisting essentially of”can be alternatively used. Where one of these three terms is used, thepresently disclosed and claimed subject matter can include the use ofeither of the other two terms.

Throughout this application, where publications are referenced, thedisclosures of these publications in their entireties are herebyincorporated by reference into this application to more fully describethe state of the art to which this present disclosure pertains.

The following detailed description is merely exemplary in nature and isnot intended to limit the present disclosure or the application and usesof the present disclosure. Furthermore, there is no intention to bebound by any theory presented in the preceding background or thefollowing detailed description.

Referring now to the drawings, there is schematically illustrated inFIGS. 1A-1B a first embodiment of a vehicle brake system, indicatedgenerally at 10. All valves of the brake system 10 are entirely disposedwithin the HCU which is configured to drive valves. The brake system 10is a hydraulic boost braking system in which boosted fluid pressure isutilized to apply braking forces for the brake system 10. The brakesystem 10 may suitably be used on a ground vehicle such as an automotivevehicle having four wheels with a wheel brake associated with eachwheel. Furthermore, the brake system 10 can be provided with otherbraking functions such as anti-lock braking (ABS) and other slip controlfeatures to effectively brake the vehicle, as will be discussed below.

The brake system 10 generally includes a first block or brake pedal unitassembly, indicated by broken lines 12, and a second block or hydrauliccontrol unit, indicated by broken lines 14. The various components ofthe brake system 10 are housed in the brake pedal unit assembly 12 andthe hydraulic control unit 14. As indicated, the brake pedal unitassembly 12 does not implement any valves. The brake pedal unit assembly12 and the hydraulic control unit 14 may include one or more blocks orhousings made from a solid material, such as aluminum, that has beendrilled, machined, or otherwise formed to house the various components.Fluid conduits may also be formed in the housings to provide fluidpassageways between the various components. The housings of the brakepedal unit assembly 12 and the hydraulic control unit 14 may be singlestructures or may be made of two or more parts assembled together. Asschematically shown, the hydraulic control unit 14 is located remotelyfrom the brake pedal unit assembly 12 with hydraulic lines hydraulicallycoupling the brake pedal unit assembly 12 and the hydraulic control unit14.

The brake pedal unit assembly 12 cooperatively acts with the hydrauliccontrol unit 14 for actuating wheel brakes 16 a, 16 b, 16 c, and 16 d.The wheel brakes 16 a, 16 b, 16 c, and 16 d can be any suitable wheelbrake structure operated by the application of pressurized brake fluid(or pressure medium). The wheel brake 16 a, 16 b, 16 c, and 16 d mayinclude, for example, a brake caliper mounted on the vehicle to engage africtional element (such as a brake disc) that rotates with a vehiclewheel to effect braking of the associated vehicle wheel. The wheelbrakes 16 a, 16 b, 16 c, and 16 d can be associated with any combinationof front and rear wheels of the vehicle in which the brake system 10 isinstalled. For example, for a vertically split system, the wheel brakes16 a and 16 d may be associated with the wheels on the same axle. For adiagonally split brake system, the wheel brakes 16 a and 16 b may beassociated with the front wheel brakes.

The brake pedal unit assembly 12 includes a fluid reservoir 18 forstoring and holding hydraulic fluid for the brake system 10. The fluidwithin the reservoir 18 may be held generally at atmospheric pressure orcan store the fluid at other pressures if so desired. The brake system10 may include a fluid level sensor 19 for detecting the fluid level ofthe reservoir. The fluid level sensor 19 may be helpful in determiningwhether a leak has occurred in the system 10.

The brake pedal control unit assembly 12 includes a brake pedal unit(BPU), indicated generally at 20. It should be understood that thestructural details of the components of the brake pedal unit 20illustrate only one example of a brake pedal unit 20. The brake pedalunit 20 could be configured differently having different components thanthat shown in FIGS. 1A-1B.

The brake pedal unit 20 includes a housing 24 having various boresformed in for slidably receiving various cylindrical pistons and othercomponents therein. The housing 24 may be formed as a single unit orinclude two or more separately formed portions coupled together. Thehousing 24 generally includes a bore 32. Bore 32 may have varyingdiameters as shown in FIGS. 1A-1B. The brake pedal unit 20 furtherincludes an input piston (or primary piston) 34 and an output piston (orsecondary piston) 40. The input piston 34 and the output piston 40 maybe slidably disposed in the bore 32.

A brake pedal, indicated schematically at 42 in FIGS. 1A-1B, is coupledto a first end 44 of the input piston 34 via an input rod 45. The inputrod 45 can be coupled directly to the input piston 34 or can beindirectly connected through a coupler (not shown). In the rest positionshown in FIG. 1A, an outer cylindrical surface 57 of the input piston 34is engaged with a seal 58 and a lip seal 60 mounted in grooves formed inthe housing 24. The input piston 34 includes a central bore 62 formedthrough the second end 52. The brake pedal unit 20 is in a “rest”position as shown in FIG. 1A. The conduit 66 is also in fluidcommunication with a first output pressure chamber 26 formed in thehousing 24. The conduit 66 is in fluid communication with a reservoirport 70 connected to the reservoir 18. A filter (not shown) may bedisposed in the port 70 or the conduit 66. The conduit 66 can be formedby various bores, grooves and passageways formed in the housing 24.

The pedal simulator 100 includes a chamber, a spring 130 and a piston22. It should be understood that that the various springs of the pedalsimulator 100 may have any suitable spring coefficient or spring rate.The simulation chamber 63 may have brake fluid and may be in fluidcommunication with a conduit 47 which is in fluid communication with thesimulation valve 74. It is understood that region 68 is the dry regionof the simulation chamber 63 because region 68 is the other side of thesimulator piston). A filter (not shown) may be housed within the conduit47. Simulator test valve 82 is also provided in the hydraulic controlunit 14 so that the two-way flow of the simulator valve 74 may beindependently opened or closed without causing the brake fluid to flowback into the master cylinder pressure chamber and/or reservoir.

As discussed above, the brake pedal unit 20 includes the input andoutput pistons 34 and 40 that are disposed in bore 32 which is formed inthe housing 24. The input and output pistons 34 and 40 are generallycoaxial with one another. A secondary output conduit 56 is formed in thehousing 24 and is in fluid communication with the second output pressurechamber 28. The secondary output conduit 56 may be extended via externalpiping or a hose connected to the housing 24. A primary output conduit66 is formed in the housing 24 and is in fluid communication with thefirst output pressure chamber 26. The primary output conduit 66 may beextended via external piping or a hose connected to the housing 24. Aswill be discussed in detail below, leftward movement of the input andoutput pistons 34 and 40, as viewing FIGS. 1A-1B, provides pressurizedfluid out through the secondary output conduit 56 and the primary outputconduit 66. A return spring 51 is housed in the first output pressurechamber 26 and biases the input piston 34 in the rightward direction.

The output piston 40 is slidably disposed in the bore 32. A secondoutput pressure chamber 28 is generally defined by the bore 32, theoutput piston 40, and the lip seal 54. Leftward movement of the outputpiston 40 causes a buildup of pressure in the second output pressurechamber 28. The second output pressure chamber 28 is in fluidcommunication with the secondary output conduit 56 such that pressurizedfluid is selectively provided to the hydraulic control unit 14. Secondoutput pressure chamber 28 is in selective fluid communication with aconduit 64 which is in fluid communication with the reservoir 18.

A first output pressure chamber 26 is generally defined by the bore 32,the input piston 34, the output piston 40, the lip seal 60, and the seal53. Although the various seals shown in the drawings are schematicallyrepresented as O-ring or lip seals, it should be understood that theycan have any configuration. Leftward movement of the input piston 34causes a buildup of pressure in the first output pressure chamber 26.The first output pressure chamber 26 is in fluid communication with theprimary output conduit 66 such that pressurized fluid is selectivelyprovided to the hydraulic control unit 14.

Referring again to FIGS. 1A-1B, the system 10 may further include atravel sensor 76 for producing a signal that is indicative of the lengthof travel of the input piston 34 which is indicative of the pedaltravel. The system 10 may also include a switch 152 for producing asignal for actuation of a brake light and to provide a signal indicativeof movement of the input piston 34. The brake system 10 may furtherinclude sensors such as pressure transducers for monitoring the pressurein the conduit 56.

The system 10 further includes a source of pressure in the form of aplunger assembly, indicated generally at 130. As will be explained indetail below, the system 10 uses the plunger assembly 130 to provide adesired pressure level to the wheel brakes 16 a-d during a normalboosted brake apply. Fluid from the wheel brakes 16 a-16 d may bereturned to the plunger assembly 130 or diverted to the reservoir 18.

The system 10 further includes a primary 3-way valve 38 and a secondary3-way valve 36 (or referred to as switching valves or base brakevalves). The three-way valves 36 and 38 may be solenoid actuatedthree-way valves. The three-way valves 36 and 38 are generally operableto up to three positions, as schematically shown in FIGS. 1A-1B. It isunderstood that three-way valve 38 is hydraulically moved to a “third”position during self-diagnostic testing as described herein. Thesecondary 3-way valve 36 has a port 36 a in selective fluidcommunication with the secondary output conduit 56 which is in fluidcommunication with the second output pressure chamber 28. A port 36 b isin fluid communication with a boost conduit 160. A port 36 c is in fluidcommunication with a conduit 48 which is selectively in fluidcommunication with the wheel brakes 16 a and 16 d. The primary 3-wayvalve 38 has a port 38 a in selective fluid communication with theconduit 66 which is in fluid communication with the first outputpressure chamber 26. A port 38 b is in fluid communication with theboost conduit 160. A port 38 c is in fluid communication with a conduit72 which is selectively in fluid communication with the wheel brakes 16b and 16 c.

The system 10 further includes various valves (slip control valvearrangement) for permitting controlled braking operations, such as ABS,traction control, vehicle stability control, and regenerative brakingblending. A first set of valves includes an apply valve 78 and a dumpvalve 80 in fluid communication with the conduit 48 for cooperativelysupplying brake fluid received from the plunger assembly 130 to thewheel brake 16 d, and for cooperatively relieving pressurized brakefluid from the wheel brake 16 d to the reservoir conduit 18 via thereservoir conduit 96. A second set of valves include an apply valve 84and a dump valve 86 in fluid communication with the conduit 48 forcooperatively supplying brake fluid received from the plunger assembly130 to the wheel brake 16 a, and for cooperatively relieving pressurizedbrake fluid from the wheel brake 16 a to the reservoir conduit 96. Athird set of valves include an apply valve 88 and a dump valve 90 influid communication with the conduit 72 for cooperatively supplyingbrake fluid received from the plunger assembly 130 to the wheel brake 16c, and for cooperatively relieving pressurized brake fluid from thewheel brake 16 c to the reservoir conduit 96. A fourth set of valvesinclude an apply valve 92 and a dump valve 94 in fluid communicationwith the conduit 72 for cooperatively supplying brake fluid receivedfrom plunger assembly 130 to the wheel brake 16 b, and for cooperativelyrelieving pressurized brake fluid from the wheel brake 16 b to thereservoir conduit 96.

As stated above, the system 10 includes a source of pressure in the formof the plunger assembly 130 to provide a desired pressure level to thewheel brakes 16 a-d. The system 10 further includes a venting valve 132and a pumping valve 134 which cooperate with the plunger assembly 130 toprovide boost pressure to the boost conduit 160 for actuation of thewheel brakes 16 a-16 d. The venting valve 132 and the pumping valve 134may be solenoid actuated valves movable between open positions andclosed positions. In the closed position, the venting valve 132 and thepumping valve 134 may still permit flow in one direction asschematically shown as a check valve in FIGS. 1A-1B. The venting valve132 is in fluid communication with a first output conduit 136 which isin fluid communication with the plunger assembly 130. A second outputconduit 138 is in fluid communication between the plunger assembly 130and the boost conduit 160.

The plunger assembly 130 includes a housing 104 having a multi-steppedbore 118 formed therein. A piston 110 is slidably disposed with the bore118. The piston 110 includes an enlarged end portion 112 connected to asmaller diameter central portion 114. The piston 110 has a second end116 connected to a ball screw mechanism, indicated generally at 120. Theball screw mechanism 120 is provided to impart translational or linearmotion of the piston 110 along an axis defined by the bore 118 in both aforward direction (leftward as viewing FIGS. 1A-1B), and a rearwarddirection (rear/right-ward as viewing FIGS. 1A-1B) within the bore 118of the housing 104. In the embodiment shown, the ball screw mechanism120 includes a motor 122 rotatably driving a screw shaft 124. The motor122 may include a sensor 126 for detecting the rotational position ofthe motor 122 and/or ball screw mechanism 120 which is indicative of theposition of the piston 110. The second end 116 of the piston 110includes a threaded bore and functions as a driven nut of the ball screwmechanism 120. The ball screw mechanism 120 includes a plurality ofballs that are retained within helical raceways formed in the screwshaft 124 and the threaded bore of the piston 110 to reduce friction.Although a ball screw mechanism 120 is shown and described with respectto the plunger assembly 130, it should be understood that other suitablemechanical linear actuators may be used for imparting movement of thepiston 110. It should also be understood that although the piston 110functions as the nut of the ball screw mechanism 120, the piston 110could be configured to function as a screw shaft of the ball screwmechanism 120. Of course, under this circumstance, the ball nut wouldrotate and the screw shaft would translate so as to move the plunger 110relative to the multi-stepped bore 118 as the ball nut is rotated viathe motor 122.

As will be discussed in detail below, the plunger assembly 130 canprovide boosted pressure to the boost conduit 160 when actuated in boththe forward and rearward directions. The plunger assembly 130 includes aseal 140 mounted on the enlarged end portion 112 of the piston 110. Theseal 140 slidably engages with the inner cylindrical surface of the bore118 as the piston 110 moves within the bore 118. A pair of seals 142 and144 is mounted in grooves formed in the bore 118. The seals 142 and 144slidably engage with the outer cylindrical surface of the piston 110. Afirst pressure chamber 150 is generally defined by the bore 118, theenlarged end portion 112 of the piston 110, and the seal 140. A secondpressure chamber 151, located generally behind the enlarged end portion112 of the piston 110, is generally defined by the bore 118, the seals142 and 140, and the piston 110. The seals 140, 142, and 144 can haveany suitable seal structure. In one embodiment, the seal 140 is a quadring seal. Although a lip seal may also be suitable for the seal 140, alip seal is more generally more compliant and requires more volumedisplacement for a given pressure differential. This may result in asmall boost pressure reduction when the piston 110 travels in therearward direction during a pumping mode. The lip seal or seal 140 maybe provided in the form of an o-ring energized PTFE seal because thiscomponent can tolerate big extrusion gaps.

As shown in FIGS. 1A-1B, the hydraulic control unit 14 also includes asimulator test valve 82 and a simulator valve 74 which may be mountedproximate to the brake simulator. The simulator test valve 82 isgenerally not used during a normal boosted brake apply or even for amanual push-through mode. The simulator test valve may be energized orde-energized during various testing modes to determine the correctoperation of the brake system 10. The simulator test valve 82 may beenergized to a “closed position” (uni-directional flow within the valve82) to prevent venting pressure medium away from the primary outputchamber via the conduit 66 such that a pressure build up in conduit 160can be used to monitor fluid (or pressure medium) flow to determine ifleaks may be occurring through seals of various components of the brakesystem 10.

As schematically shown in FIGS. 1A-1B, the simulation valve 74 may be asolenoid actuated valve. The simulation valve 74 includes a first port75 and a second port 77. The first port 75 is in fluid communicationwith the conduit 47 and the simulation chamber 63 of the simulator 100.The second port 77 is in fluid communication with the reservoir 18 viathe conduits 66 and 70. The simulation test valve 82 is movable betweena first open (de-energized) position allowing the flow of fluid from thesimulation chamber 63 to the first output pressure chamber 26, and asecond closed position blocking flow of fluid or pressure medium betweenthe first output pressure chamber 26 and the simulation chamber 63 onlyin direction from simulator to master cylinder. The simulation valve 74is in the first closed position or normally closed position when notactuated (not energized) such that fluid is prevented from flowing intothe simulation chamber 63 through conduit 160.

The simulator valve 74 may be energized together with the apply valves78, 84, 92, 88 and while the simulator test valve 82 is energized (so asto close/block pressure medium from flowing from conduit 160 to conduit66) and the simulator valve 74 is energized so as to open simulatorvalve 74 (to increase fluid flow through simulator valve 74) so that thedual acting plunger 110 can be used to fill the pedal simulator 100 viaconduit 160 with the pressure medium so that the system may performself-diagnostic tests as later described herein. Under thiscircumstance, the secondary 3-way valve and the pumping valve are alsoenergized.

Example, non-limiting diagnostic operations of the aforementioned systemmay include: (1) a diagnostic test for a leak in the Simulator Valve;(2) an optional diagnostic test for a leak in the Pedal Simulator;and/or (3) a diagnostic test for a leak in the primary and/or secondarythree-way valves.

In order to perform a diagnostic test for a leak in the simulator valve74 in the example system of FIG. 1A, the system 10 may perform thefollowing steps: (1) energize the secondary three-way valve 36, thepumping valve 134, the simulator test valve 82, and the apply valves 78,84, 88, 92 in order to maintain brake fluid from the plunger assembly130 within the boost circuit 160; (2) Apply the dual acting plunger 110in the plunger assembly 130 to a predetermined pressure level such as 30Bar in the boost circuit 160 wherein the boost pressure sensor 148 isused to determine the pressure level in the boost circuit 160; (3) Holdthe plunger 110 in position within the plunger assembly and if thepressure in the boost circuit 160 deteriorates at or more than apre-determined rate (ex: more than 20 Bar in 100 msec), then identify aleak in the simulator valve 74 via a signal from the ECU 106 to avehicle user interface 108. Alternatively, if the plunger 110 has totravel more than a pre-determined distance (ex: 4 mm) in order toachieve a pressure of 30 Bar in the boost circuit 160 (at step 2), thenidentify a leak in the simulator valve 74 via a signal 146 from the ECU106 to a vehicle user interface 108.

Following the test for a leak in the simulator valve 74 and withreference to FIG. 1B, the system 10 may perform another diagnostic testfor a leak in the pedal simulator 100 by performing the following steps:(1) de-energize the simulator test valve 82 to release pressure; (2)energize the pedal simulator valve 74 and then energize the simulatortest valve 82; (3) apply the dual acting plunger 110 (while energizingthe secondary three-way valve 36, the pumping valve 134, the simulatortest valve 82, and the apply valves 78, 84, 88, 92) to achieve apredetermined pressure in the pedal simulator 100; (4) hold the dualacting plunger 110 in position once the predetermined pressure has beenachieved in the pedal simulator and if the pressure in the in the pedalsimulator 100 deteriorates at a pre-determined rate (ex: more than 3 Barin 100 msec), then identify a leak in the pedal simulator 100 via asignal 146 from the ECU 106 to a vehicle user interface 108.Alternatively, if the dual acting plunger 110 in the plunger assembly130 has to travel more than a pre-determined distance (ex: 5 mm to 20mm) in order to achieve a pressure of 10 Bar in the pedal simulator (atstep 3) then identify a leak in the pedal simulator 100 via a signal 146from the ECU 106 to a vehicle user interface 108.

Following the test of the pedal simulator 100 for leaks, theabove-referenced system 10 may also test for a leak in the three-wayvalves 36, 38. However, in the event a leak has been detected in thepedal simulator 100, any boost pressure from the previous test must bereleased before testing for a leak in the three-way valves 36, 38.Accordingly, such boost pressure may be released from the boost circuit160 by de-energizing the simulator test valve 82 and moving the plunger110 to the home position. In contrast, if a leak has not been detectedin the pedal simulator 100, then the aforementioned boost pressurerelease is not required.

Once the boost pressure has been reduced in the boost circuit 160, themethod for testing for a leak in the three way valves includes thefollowing steps: (1) fill the pedal simulator 100 using the same methodused as was used in the aforementioned simulator leak detectionprocess/method; (2) De-energize the secondary 3-way valve and thenretract the dual acting plunger to the home position to further drop thepressure in the boost circuit to zero while also monitoring the mastercylinder secondary pressure sensor 98 (which is indicative of pressureat the output of the fluid separator 156 during this test method); (3)Determine whether there is a pressure reduction at the secondary mastercylinder pressure sensor 98. If the pressure deteriorates at apre-determined rate (more than 7 bar in 100 msec), then then identify aleak in the three-way valves 36, 38 via a signal from the ECU to avehicle user interface. However, if the pressure drop does not exceedthe predetermined threshold, then the HCU determines that there is not aleak in either of the three-way valves 36, 38.

Referring now to FIGS. 2A-2B, an orifice (see element 30) may beimplemented at the master cylinder 50 (in the conduit 67 between theventing port 154 of the first output pressure chamber 26 and thereservoir 18) instead of using a simulator test valve (see element 82 inFIGS. 1A and 1B) in the brake module (see element 14 in FIGS. 1A-1B).The system 128 shown in FIGS. 2A-2B may perform the following steps todetermine if there is a leak in the simulator valve 74 (shown in FIGS.2A-2B): (1) provide a simulator 100 (see FIG. 2A) which is onlypartially full of pressure medium and a de-energized simulator valve 74;(note: when de-energized, the simulator valve 74 only allows fluid toflow in one direction—from the simulator 100 towards conduit 66, butwhen energized, the simulator valve 74 may, but not necessarily, permitfluid to flow in both directions) (2) Energize the pumping valve 134,the secondary three way valve 36, and the apply valves 78, 84, 92, 88 sothat all apply valves 78, 84, 92, 88 are closed (where pressure mediumis only able to flow from the dump valves 80, 86, 94, 90 towards thecorresponding three way valve 36, 38); (3) apply and retract the dualacting plunger (or piston) 110 in the plunger assembly 130 so that apredetermined pressure is achieved at the master cylinder secondarypressure sensor 98; (4) Hold the plunger 110 in position, but maintainthe replenishing check valve 102 in a closed position this automaticallyhappens when the plunger stops moving (to prevent pressure medium fromflowing from the plunger assembly 130 to reservoir 18) while energizingthe simulator valve 74 (to enhance medium flow from the simulatorchamber 63 towards the orifice 30); (5) Measure master cylindersecondary pressure decay to obtain the measured master cylindersecondary pressure decay; (6) Compare measured master cylinder secondarypressure decay to a predetermined master cylinder secondary pressuredecay value. (The predetermined master cylinder secondary pressure decayvalue may be taken from a master cylinder secondary pressure decay rateobtained when the system was new and the application of the mastercylinder was used to verify that the simulator valve did not leak); (7)If the measured master cylinder secondary pressure decay does not matchthe predetermined master cylinder secondary pressure decay, then thenidentify a leak in the simulator valve via a signal from the ECU to avehicle user interface. (8) De-energize all the valves. It is understoodthat the system may optionally indicate that there is no leak in thesimulator valve via a signal from the ECU to a vehicle user interface ifthe measured master cylinder secondary pressure decay does match thepredetermined master cylinder secondary pressure decay.

In step 1 of the aforementioned method, the simulator 100 may bepartially filled with pressure medium by energizing the pumping valve134, the secondary three way valve 36, and the apply valves 78, 84, 92,88 and then applying and retracting the plunger in the plunger assembly(while keeping the simulator valve open or energized) until the pressurein the second output pressure chamber of the master cylinder reads about1.5 bar and then de-energize the simulator valve while completing thestroke of the plunger in the plunger assembly.

While various example, non-limiting embodiments have been presented inthe foregoing detailed description, it should be appreciated that a vastnumber of variations exist. It should also be appreciated that theexemplary embodiments are only examples, and are not intended to limitthe scope, applicability, or configuration of the disclosure in any way.Rather, the foregoing detailed description will provide those skilled inthe art with a convenient road map for implementing the exemplaryembodiment or exemplary embodiments. It should be understood thatvarious changes can be made in the function and arrangement of elementswithout departing from the scope of the disclosure as set forth in theappended claims and the legal equivalents thereof.

What is claimed is:
 1. A diagnostic method to identify a leak in athree-way valve for a vehicle brake system comprising the steps of:providing a pedal simulator having a pressure medium within a simulationchamber of the pedal simulator; de-energizing a secondary three-wayvalve retracting a plunger to a home position within a plunger assemblyto reduce boost circuit pressure to zero while also monitoring pressureat an output of a fluid separator via a secondary master cylinderpressure sensor; determining a rate of pressure reduction at the outputof a fluid separator via the secondary master cylinder pressure sensor;and identifying a leak in at least one of a primary three-way valve andthe secondary three-way valve if the rate of pressure reduction is equalto or greater than a pre-determined rate, wherein the step of providingthe pedal simulator having pressure medium includes the steps of:energizing a pumping valve, the secondary three-way valve, and aplurality of apply valves; energizing a simulator valve to enablebi-directional flow of pressure medium within the simulator valve;applying and retracting the plunger in the plunger assembly whilekeeping the simulator valve energized, until pressure within a secondoutput pressure chamber of a master cylinder reaches a pre-determinedlevel; and de-energizing the simulator valve while completing the strokeof the plunger in the plunger assembly once pressure in the secondoutput pressure chamber of the master cylinder reaches the predeterminedlevel.
 2. The diagnostic method as defined in claim 1 wherein areservoir and the master cylinder of the vehicle brake system isdisposed in a first module while the pedal simulator, a simulator testvalve, and the plunger assembly of the vehicle brake system are disposedin a second module which is separate from the first module.
 3. Thediagnostic method as defined in claim 1 wherein the pre-determined rateis about 7 bar in 100 msec.
 4. The diagnostic method as defined in claim1 wherein the step of identifying a leak in at least one of the primaryand secondary three-way valves is performed via a signal transmittedfrom an ECU to a vehicle user interface.
 5. The diagnostic method asdefined in claim 1 wherein the pre-determined pressure level for thesecond output pressure chamber is about 1.5 bar.
 6. The diagnosticmethod as defined in claim 2 wherein the second module of the vehiclebrake system houses every hydraulic valve of the vehicle brake system.7. The diagnostic method as defined in claim 1 wherein the pressuremedium is brake fluid.
 8. The diagnostic method as defined in claim 1wherein the plunger assembly includes a motor which is actuated by anelectronic control module and the motor causes the plunger in theplunger assembly to cycle within a first pressure chamber in the plungerassembly.
 9. The diagnostic method as defined in claim 8 wherein theprimary three-way valve is in fluid communication with a second wheelbrake and a third brake while the secondary three-way valve is in fluidcommunication with a first wheel brake and a fourth wheel brake.